Fast-forward fall

Even though Illinois recently received a break from this summer’s heat and drought, the precipitation deficit that remains statewide has kicked off autumn with atypical natural events. Thus far, the year 2012 has been the fourth driest on Illinois record. However, it has been raining acorns and fall colors have been peeking through the greenery since late August—three weeks earlier than usual. This fast-forward to fall is a tree’s way of protecting itself when water is in short supply. The vibrant color displays of autumn, which seem so lively, are actually a sign that a tree is entering dormancy.

These flashes of fall colors are a result of changes in pigments. The dominant green pigment in leaves is chlorophyll. The leaves in a tree are like little factories, mixing together a recipe of specific ingredients (sunlight, carbon dioxide and water) to make food for the tree’s growth. Chlorophyll acts as the “chef” in this process, called photosynthesis; its presence is necessary in bringing everything together.

Typically, autumn’s cool nights and shortening days trigger photosynthesis to slow down. The scarcity of one key ingredient, water, is triggering this earlier-than-average dormancy. As the work of the leaves comes to an end for the year, chlorophyll breaks down and reveals yellow and orange pigments that have hidden behind its green cloak all summer. Leaves that contain the pigments xanthophyll and carotene—as do hickories, cottonwoods, elms and some maples—will change to vivid shades of yellow and orange as the green fades. Continue reading